PROMOTION EFFECT OF K2O AND MNO ADDITIVES ON THE SELECTIVE PRODUCTION OF LIGHT ALKENES VIA SYNGAS OVER FE/SILICALITE-2 CATALYSTS

The addition of K2O and MnO promoters enhances catalyst activity and selectivity to light alkenes during CO hydrogenation over silicate-2 (Si-2) supported Fe catalysts. The results of CO hydrogenation and CO-TPD, CO/H-2-TPSR, C2H4/H-2-TPSR and C2H4/H-2 pulse reaction over Fe/Si-2 catalysts with and without promoters clearly show that the MnO promoter mainly prohibits the hydrogenation of C2H4 and C3H6. Therefore, it enhances the selectivity to C2H4 and C3H6 products. Meanwhile further incorporating the K2O additive into the FeMn/Si-2 catalyst leads to a remarkable increase in both the capacity and strength of the strong CO adspecies. These produce much more [C-ad] via their dissociation and disproportionation at higher temperatures. This results in an increase in the CO conversion and the selectivity to light olefins. Moreover, the K2O additive modifies the hydrogenating reactivity of [C-ad] and suppresses the disproportionation of C2H4 that occurs as a side-reaction. Both K2O and MnO promoters play key roles for enhancing the selective production of light alkenes from CO hydrogenation over Fe/Si-2 catalyst